It is well known in the art to use raised contact elements (sometimes referred to as "bumps") to make contact for electrical interconnection. Such bump contacts are frequently used on interconnect devices or circuitry that is used to connect a circuit to an electronic component or to another circuit. By way of example, it is known to use bump contacts to connect one circuit component to another, often by the use of a pressure connection system such as shown, e.g., in U.S. Pat. Nos. 4,468,074, 4,610,495, and 4,768,971. For example, it is known to use contact bumps on flexible circuitry to connect to circuit boards via a pressure connection. Uniformity of bump height is not crucial in many such applications because the flexibility of the circuitry and the distance between bump sites allows the device a degree of conformity to make the contacts. However, that is not true when the density of bump contact increases and the bumps come closer together. In such cases the flexibility of the interconnect circuit material may not provide the needed compensation to overcome differences in bump height, and malfunctions will occur because of failure to make contact where required.
When bump contacts are used in a high density contact applications, such as multichip module (MCM) to circuit board connections (e.g., pitch (center to center of adjacent contact sites) under 50 mils), it is extremely important that coplanarity of the bump contact surfaces be maintained. That is, the height of the bumps must be carefully controlled so that the top or contact surfaces of all of the bumps will be in the same plane in order to make contact with the contact points on the MCM or other device to be contacted. If the bump height differs from bump to bump, contact may not be established at all contact sites. For example, if a shorter bump is located between two higher bumps, the shorter bump may not make contact with its intended contact site on the MCM or other device, thereby resulting in a malfunction.
The need for bump coplanarity, especially in high density interconnect applications, is recognized in the art, but it has heretofore been difficult to achieve that objective. The present invention presents an effective and reliable way to achieve coplanar bump contacts.